Metastasis is one of the most relevant negative prognostic indicators for many types of cancer. We hypothesized that CDK5 activity, which controls neuronal migration during brain neocortical development, also may control metastasis in some cancers. We have found that CDK5, heretofore thought to be active mainly in neuronal lineages, is active in several types of cancer, due to expression of its activator protein p35. Blocking CDK5 activity resulted in inhibition of cancer cell motility and invasion, and, in a prostate cancer model, a 79% decrease in spontaneous metastasis. This indicates that CDK5 activity may be a central control for metastasis, and CDK5 may be a potential therapeutic target to limit metastasis. This application will explore the role of CDK5 in metastasis, and its function in the biology of cancer. In Specific Aim 1, a genetically engineered animal model for the role of CDK5 in metastasis and tumor biology will be developed. The effect of Cdk5 ablation on tumor growth, differentiation, angiogenesis, immune response, and, especially, metastasis will be investigated. Potential pathways for escape from Cdk5 ablation-mediated inhibition of metastasis will be explored. In Specific Aim 2, the functions of CDK5 in cancer will be explored, using gene expression analysis of CDK5 inhibition in prostate cancer. Advanced biostatistical analysis methods will be applied to microarray gene expression data, to look for transcription signatures that may predict mechanisms of control of metastasis, as well as novel functions of Cdk5 in tumor biology, and potential sensitization to other therapies. Data analysis methods will include GSEA, Bayesian Decomposition, and other analytical tools, including analytical methods under development in Dr. Ochs's group. Functional biological analyses will be employed to confirm predictions derived from these analyses of transcriptional signatures. In Specific Aim 3, the mechanism of receptor tyrosine kinase control of p35 expression will be explored. We will confirm that ErbB-family mediated activation of p35 is at the transcriptional level, and then identify the transcription factor(s) that mediate this induction. The effect of the identified transcription factor on p35 expression will be examined, using gene transfer and siRNA. The correlation of expression of the identified transcription factor with p35 expression will be examined in a panel of cell lines. Narrative: In many types of cancer, metastatic spread is closely linked to lethality, and control of metastasis may be an important step in increasing survival. We have identified a cellular enzyme, CDK5, whose activity appears to be required for metastasis in prostate and other cancers. This project seeks to define the role of CDK5, a potential therapeutic target, in control of metastasis and tumor function.